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Re: PATCH for 64-bit MIPS ELF buglets
Here's a patch (checked in) which attempts to restore R_MIPS16_26
relocation support. (Not the stub functionality, just the relocation.)
Ian, please check this over, especially the code in
mips_elf_perform_relocation.
Thank you,
--
Mark Mitchell mark@codesourcery.com
CodeSourcery, LLC http://www.codesourcery.com
1999-07-13 Mark Mitchell <mark@codesourcery.com>
* elf32-mips.c (mips_elf_calculate_relocation): Handle R_MIPS16_26.
(mips_elf_relocate_section): Adjust calling sequence for
mips_elf_perform_relocation.
(mips_elf_perform_relocation): Take additional argument. Handle
R_MIPS16_26. Use bfd_put for convenience.
Index: elf32-mips.c
===================================================================
RCS file: /cvs/binutils/binutils/bfd/elf32-mips.c,v
retrieving revision 1.21
diff -u -p -r1.21 elf32-mips.c
--- elf32-mips.c 1999/07/13 18:21:19 1.21
+++ elf32-mips.c 1999/07/14 06:52:14
@@ -170,7 +170,8 @@ static bfd_reloc_status_type mips_elf_ca
static bfd_vma mips_elf_obtain_contents
PARAMS ((reloc_howto_type *, const Elf_Internal_Rela *, bfd *, bfd_byte *));
static void mips_elf_perform_relocation
- PARAMS ((reloc_howto_type *, const Elf_Internal_Rela *, bfd_vma,
+ PARAMS ((struct bfd_link_info *, reloc_howto_type *,
+ const Elf_Internal_Rela *, bfd_vma,
bfd *, bfd_byte *));
static boolean mips_elf_assign_gp PARAMS ((bfd *, bfd_vma *));
static boolean mips_elf_sort_hash_table_f
@@ -5883,6 +5884,12 @@ mips_elf_calculate_relocation (abfd,
value &= howto->dst_mask;
break;
+ case R_MIPS16_26:
+ /* The calculation for R_MIPS_26 is just the same as for an
+ R_MIPS_26. It's only the storage of the relocated field into
+ the output file that's different. That's handle in
+ mips_elf_perform_relocation. So, we just fall through to the
+ R_MIPS_26 case here. */
case R_MIPS_26:
if (local_p)
value = (((addend << 2) | (p & 0xf0000000)) + symbol) >> 2;
@@ -5922,7 +5929,7 @@ mips_elf_calculate_relocation (abfd,
Here $t9 holds the address of the function being called,
as required by the MIPS ELF ABI. The R_MIPS_LO16
- relocation can easily overlfow in this situation, but the
+ relocation can easily overflow in this situation, but the
R_MIPS_HI16 relocation will handle the overflow.
Therefore, we consider this a bug in the MIPS ABI, and do
not check for overflow here. */
@@ -6037,7 +6044,6 @@ mips_elf_calculate_relocation (abfd,
/* We don't do anything with these at present. */
return bfd_reloc_continue;
- case R_MIPS16_26:
case R_MIPS16_GPREL:
/* These relocations, used for MIPS16, are not clearly
documented anywhere. What do they do? */
@@ -6107,7 +6113,9 @@ mips_elf_obtain_contents (howto, relocat
Returns false if anything goes wrong. */
static void
-mips_elf_perform_relocation (howto, relocation, value, input_bfd, contents)
+mips_elf_perform_relocation (info, howto, relocation, value,
+ input_bfd, contents)
+ struct bfd_link_info *info;
reloc_howto_type *howto;
const Elf_Internal_Rela *relocation;
bfd_vma value;
@@ -6115,48 +6123,105 @@ mips_elf_perform_relocation (howto, relo
bfd_byte *contents;
{
bfd_vma x;
- bfd_byte *location = contents + relocation->r_offset;
+ bfd_byte *location;
+
+ /* Figure out where the relocation is occurring. */
+ location = contents + relocation->r_offset;
/* Obtain the current value. */
x = mips_elf_obtain_contents (howto, relocation, input_bfd, contents);
/* Clear the field we are setting. */
x &= ~howto->dst_mask;
-
- /* Set the field. */
- x |= (value & howto->dst_mask);
-
- /* Put the value into the output. */
- switch (bfd_get_reloc_size (howto))
- {
- case 0:
- x = 0;
- break;
- case 1:
- bfd_put_8 (input_bfd, x, location);
- break;
+ /* If this is the R_MIPS16_26 relocation, we must store the
+ value in a funny way. */
+ if (ELF32_R_TYPE (relocation->r_info) == R_MIPS16_26)
+ {
+ /* R_MIPS16_26 is used for the mips16 jal and jalx instructions.
+ Most mips16 instructions are 16 bits, but these instructions
+ are 32 bits.
+
+ The format of these instructions is:
+
+ +--------------+--------------------------------+
+ ! JALX ! X! Imm 20:16 ! Imm 25:21 !
+ +--------------+--------------------------------+
+ ! Immediate 15:0 !
+ +-----------------------------------------------+
+
+ JALX is the 5-bit value 00011. X is 0 for jal, 1 for jalx.
+ Note that the immediate value in the first word is swapped.
+
+ When producing a relocateable object file, R_MIPS16_26 is
+ handled mostly like R_MIPS_26. In particular, the addend is
+ stored as a straight 26-bit value in a 32-bit instruction.
+ (gas makes life simpler for itself by never adjusting a
+ R_MIPS16_26 reloc to be against a section, so the addend is
+ always zero). However, the 32 bit instruction is stored as 2
+ 16-bit values, rather than a single 32-bit value. In a
+ big-endian file, the result is the same; in a little-endian
+ file, the two 16-bit halves of the 32 bit value are swapped.
+ This is so that a disassembler can recognize the jal
+ instruction.
+
+ When doing a final link, R_MIPS16_26 is treated as a 32 bit
+ instruction stored as two 16-bit values. The addend A is the
+ contents of the targ26 field. The calculation is the same as
+ R_MIPS_26. When storing the calculated value, reorder the
+ immediate value as shown above, and don't forget to store the
+ value as two 16-bit values.
+
+ To put it in MIPS ABI terms, the relocation field is T-targ26-16,
+ defined as
+
+ big-endian:
+ +--------+----------------------+
+ | | |
+ | | targ26-16 |
+ |31 26|25 0|
+ +--------+----------------------+
+
+ little-endian:
+ +----------+------+-------------+
+ | | | |
+ | sub1 | | sub2 |
+ |0 9|10 15|16 31|
+ +----------+--------------------+
+ where targ26-16 is sub1 followed by sub2 (i.e., the addend field A is
+ ((sub1 << 16) | sub2)).
+
+ When producing a relocateable object file, the calculation is
+ (((A < 2) | (P & 0xf0000000) + S) >> 2)
+ When producing a fully linked file, the calculation is
+ let R = (((A < 2) | (P & 0xf0000000) + S) >> 2)
+ ((R & 0x1f0000) << 5) | ((R & 0x3e00000) >> 5) | (R & 0xffff) */
+
+ if (!info->relocateable)
+ /* Shuffle the bits according to the formula above. */
+ value = (((value & 0x1f0000) << 5)
+ | ((value & 0x3e00000) >> 5)
+ | (value & 0xffff));
+
+ /* Perform the relocation. */
+ x |= (value & howto->dst_mask);
- case 2:
- bfd_put_16 (input_bfd, x, location);
- break;
+ /* Swap the high- and low-order 16 bits on little-endian
+ systems. */
+ if (bfd_little_endian (input_bfd))
+ x = (((x & 0xffff) << 16)
+ | (((x & 0xffff0000) >> 16) & 0xffff));
- case 4:
+ /* Store the value. */
bfd_put_32 (input_bfd, x, location);
- break;
+ return;
+ }
- case 8:
-#ifdef BFD64
- bfd_put_64 (input_bfd, x, location);
-#else
- abort ();
-#endif
- break;
+ /* Set the field. */
+ x |= (value & howto->dst_mask);
- default:
- abort ();
- break;
- }
+ /* Put the value into the output. */
+ bfd_put (8 * bfd_get_reloc_size (howto), input_bfd, x, location);
}
/* Relocate a MIPS ELF section. */
@@ -6376,7 +6441,7 @@ _bfd_mips_elf_relocate_section (output_b
}
/* Actually perform the relocation. */
- mips_elf_perform_relocation (howto, rel, value, input_bfd,
+ mips_elf_perform_relocation (info, howto, rel, value, input_bfd,
contents);
}